If soap.wsdl_cache_enabled is on, this setting
determines the type of caching. It can be any of:
WSDL_CACHE_NONE (0),
WSDL_CACHE_DISK (1),
WSDL_CACHE_MEMORY (2) or
WSDL_CACHE_BOTH (3). This can
also be set via the options array in the
SoapClient or SoapServer
constructor.

2. max_execution_time default 30 secsThis can be the next bottleneck (but only when your default_socket_timeout is larger then this setting). Your soap server will not return anything, no faults no output, just an empty string.

If you want to dissable WSDL-caching, you can do so with
<?php
ini_set('soap.wsdl_cache_enabled', '0');
ini_set('soap.wsdl_cache_ttl', '0');
?>
However you must do this before creating a SOAP object (soap_client or soap_server).
Changing the settings like above does not have any effect on already existing soap-objects.

Keep in mind if you have memory cache enabled that even if you use an updated WSDL file, it will still be using the one in memory. If you download the WSDL files yourself, avoid using memory cache as you will have no control over it, or set the TTL to a small value (default is 1 day).